About 400 flights were delayed Sunday because of air traffic controller furloughs, the Federal Aviation Administration said, and a few more interruptions were reported Monday, though the nation's air travel system operated without serious problems thanks to light traffic and good weather.

Baltimore-Washington International Thurgood Marshall Airport saw departure delays up to 75 minutes for a time on Monday afternoon, according to FlightStats.com. It was unclear if those delays were furlough-related, but during that period air traffic controllers stopped ground traffic because arrivals were projected to exceed capacity.

Paul Wiedefeld, the airport's executive director, cautioned that the situation was fluid.

"It's coming at the worst possible time as we get into peak season and see extreme weather pop up across the country, and it could grow exponentially," Wiedefeld said. "All of us are still trying to get our arms around this, and I think we'll know more — Thursday, Friday — going into this weekend."

The FAA warned that nationwide, more delays are on the horizon as air traffic gets heavier during the week and weather puts pressure on understaffed air traffic controllers.

"Controllers will space planes farther apart so they can manage traffic with current staff, which will lead to delays at airports," the federal agency said in a statement.

At BWI, travelers are being urged to check with their airlines and the airport website for delays.

"But even that's kind of risky because things can change pretty quickly," Wiedefeld said. "The uncertainty with this is the frustrating part."

Furloughs of air traffic controllers have prompted an outcry from Washington lawmakers and litigation by pilots and airlines who say they could have been avoided. Airline workers have even started to use frustrated passengers to pressure the FAA to reconsider the budget cuts.

To help cut more than $600 million called for by budget sequestration, the FAA ordered air traffic controllers starting Sunday to take one furlough day for every two-week pay period. That would cut the nation's nearly 15,000 air traffic controllers by about 10 percent on any given day.

By Sunday evening a few airports across the country, including Los Angeles International and New York's LaGuardia Airport and John F. Kennedy International Airport, reported delays of more than an hour because of air traffic control staff shortages. By Monday, Los Angeles International officials said the airport was operating without major setbacks.

Flights were delayed Monday by an average of about 80 minutes at Kennedy and LaGuardia but the Port Authority of New York and New Jersey attributed those delays to construction work, high wind and other factors.

"There are many reasons for delays," said Ron Morisco, a spokesman for the Port Authority. He declined to comment on the specific impact of furloughs on delays.

The FAA and two airline monitoring websites showed that the nation's overall air traffic system operated close to normal for a Monday, a heavy air travel day. The exceptions were long delays attributed to air traffic control staff shortages at several airports in Florida and North Carolina.

Airlines for America, the trade group for the nation's largest airlines, joined a pilots association and operators of regional carriers in a suit filed Friday that asks the U.S. Court of Appeals for the District of Columbia Circuit to prevent job furloughs. But the court is not expected to consider the suit until later this week.

The airlines and pilots groups say the furloughs will delay as many as 6,700 flights per day.

"While we are not seeing a significant impact on operations at this point, we are experiencing delays in areas where the weather is good, which should not be the case," said Jean Medina, a spokeswoman for the airlines group.

In Washington, the FAA budget cuts prompted an outcry from critics of the Obama administration.

"We know that the FAA has the flexibility to reduce costs elsewhere, such as contracts, travel, supplies and consultants, or to apply furloughs in a manner that better protects the most critical air traffic control facilities," said Rep. Bill Shuster of Pennsylvania, the Republican chairman of the House Transportation and Infrastructure Committee. "Yet rather than take this approach, the administration has made choices that appear designed to have the greatest possible impact on the traveling public."

White House press secretary Jay Carney blamed Republicans for the cuts, calling the FAA furloughs "an unfortunate result" of botched budget negotiations in Congress. He said 70 percent of the FAA's expenses are for personnel, and that the agency could not accomplish the necessary cost reductions elsewhere.